Caulk, adhesive, potting material and other fluids are commonly contained in tubular cartridges of the type having a closure wall and nozzle at one end and an opposite open end that is closed by a wiper slidably seated against the inside of the cartridge. Dispensing tools are available to hold these cartridges, and to move a plunger axially of and into the open cartridge end and against the wiper, for discharging the contained material from the open nozzle. Available dispensing tools can be powered pneumatically or manually. Although pneumatic tools generally outperform manual tools, manual tools are yet in demand because of advantages including costs and portability compared to pneumatic tools.
Most manual dispensing tools utilize a rod connected to the plunger and a power device, such as a ratchet mechanism activated by squeezing a trigger, that incrementally indexes the rod and its connected plunger axially of the cartrigde and toward the nozzle. A user's needed strength and experienced fatigue, and poor continuity of material flow, are major shortcomings of using the broadly described manual dispensing tools.
For example, most contained materials are substantially incompressible liquids or pastes having poor flow characteristics and/or high viscosities, and frequently the material must be discharged against a significant back pressure. Thus, large axial forces must be exerted on the plunger rod to advance the plunger through the cartridge. It is possible to use different ratio ratchet mechanisms to generate greater indexing forces, but as the indexed distance and generated force will be inversely related, a major drawback against user acceptance may be the additional number of squeezes needed to provide the intended volume of material discharge.
Moreover, with substantially incompressible liquids or pastes, the plunger advance must correspond exactly to the needed rate of material discharge. Each squeezing stroke ideally would take place over a short duration, within a second or so. However, such rapid completion of a squeezing stroke could advance the plunger significantly more than needed to provide the intended material discharge rate. Consequently, it has been necessary with an indexing power device, to extend each squeezing stroke over a longer continuous duration, in order to obtain the intended material discharge rate. When large squeezing pressures are also needed approaching even the user's maximum strength, cramped muscles are commonplace when the user must maintain such squeezing pressures continuously, squeeze after squeeze.
The above factors contribute to poor continuity of material flow, where rest pauses in the manual powering effort would typically result in a pulsed material discharge. However, even though a user conscientiously tries to produce a uniform material discharge against a high back pressure, during that brief pause between each trigger squeeze, the material discharge will virtual stop to yield a pulsed discharge.
These shortcomings are intensified when the dispensing tool and/or intended discharge point must be inconveniently located relative to the user, such as when making upwardly directed material discharges or when reaching excessively.
Moreover, composite materials having very desirable physical properties frequently can be formed by blending together reactive materials according to precise proportions. Common multiple component reactive materials include two-part epoxies, urethanes, silicones, phenolics, acrylics and polyesters. Existing manual dispensing tools for such multiple component material systems utilize a separate cartridge for containing each component, and force all component discharges through a single mixing nozzle for yielding a single combined material discharge. The separate cartridges are held in adjacent side-by-side relationship, and separate plungers are advanced in unison through the respective cartridges. As the components and their ratios can be varied to yield different materials, component cartridges are available in different sizes and diameters.
The forced blending of the components before discharge increases the needed static pressures and plunger forces, as does the possible use of large diameter cartridges for yielding large volumetric capacities and/or specific component ratios. Any variation from precisely matched advances of the paired plungers could modify the desired component ratios and adversely change the expected physical properties of the resulting material. Moreover, pulsed discharge disrupts proper component mixing and/or proportioning, resulting in inconsistent material discharge possibly having unexpected inferior physical properties.